1. Field of the Invention
The present invention relates to a gas compressor, and more particularly to a scroll compressor for compressing a gas by the relative movement between a pair of scroll members.
2. Description of the Related Art
Scroll compressors using scroll members are operated in a low noise and at a high compressing efficiency as well. In general, scroll compressors each using a pair of scroll wraps are classed in the following two types:
The pair of scroll members comprise a pair of scroll wraps relatively orbiting each other.
(1) a scroll compressor in which one of the scroll wraps is orbiting with respect to the other scroll wrap; and
(2) a scroll compressor in which both scroll wraps are orbiting with respect to each other.
Both types (1) and (2) of the scroll compressors are also further classed in the following two types in view of their structure:
(A) a scroll compressor in which a bearing portion is provided on the central portion of one of the scroll wraps; and
(B) a scroll compressor in which a bearing portion does not exist on the central portion of any one of the scroll wraps.
A general scroll compressor having the bearing portion at the central portion of said one of the scroll wraps, that is, the scroll compressor of a type of (1) (A) or (2) (A) comprises a first end member and a second end member arranged to face each other and making relative movement, a bearing portion extending through the central portion of the second end member to the height of the first end member, a first scroll wrap vortically wound and extending to a surface of the first end member which faces the second end member, a second scroll wrap vortically wound and extending to a surface of the second end member, a gas compressing chamber defined between the first and second scroll wraps and forming the outer region as a low pressure region and the inner region around the bearing portion as a high pressure region, and means for relatively moving the first and second end members.
In the scroll compressor of type (A), bending moment exerted on an axis fitted on the bearing portion is rendered smaller and an auxiliary bearing is more easily provided than in the scroll compressor of type (B).
However, the scroll compressor of type (A) is encountered with the problem that it is difficult to make the volume of the pressure space at the final stage of the compressing cycle small because the bearing portion is formed at the center of the scroll wrap. Consequently, the number of turns of the scroll wraps of the scroll compressor of type (A) must be increased to obtain the same degree of the compression ratio as that of the scroll compressor of type (B), resulting in the drawbacks that the outer diameter of the overall compressor is elevated and the productivity is lowered as well.
Accordingly, the scroll compressor of type (A) must be increased in outer diameter in order to obtain a high compression ratio.